This invention relates to ducts, and more particularly to flexible ducts and method of making same.
Tubing made from thin flexible plastic film is widely used for overhead ducts to heat and ventilate greenhouses and similar structures. Such thin-walled tubing, known commercially as convection tubing, provides convenient and inexpensive ventilation and heating but is difficult to install and tends to tear easily. As the tubing is typically suspended from an overhead wire which is frequently as high as sixteen feet above the floor its installation has required climbing a ladder to affix the tubing at spaced apart points to the wire. In addition to the hazards of installation, fallen tubing can also cause serious problems. If tubing tears it can fall and crush delicate plants as well as interrupt heating and ventilation thus also causing damage to plants.
There are numerous ways to suspend tubing from a horizontal overhead wire such as by a plurality of clamp-type hangers or by loops of cord encompassing the duct and wire qirthwise. In the clamp-type hanger, a flat bar positioned inside the tubing is inserted in a channel positioned outside the tubing so that a portion of the tubing is clamped between the bar and channel. A snap ring is then inserted through an aperture in the channel and around the overhead wire to suspend the bar, channel, and tubing from the wire. Suspending the tubing with such clamp-type hangers is generally a time-consuming and tedious task. Additionally, as such hangers are relatively costly and many are required to suspend the tubing, use of such hangers is somewhat expensive. While the use of spaced apart loops of cord is less expensive, the installation is time-consuming and as with the other known ways of suspending the duct the installation requires the use of ladders.